The present invention relates to a technology for monitoring cardiopulmonary activity signals, and more particularly, to a non-contact apparatus and method for monitoring cardiopulmonary activity signals
Breathing disorders commonly occur in premature infants, which manifest themselves in symptoms such as apnea or intermittent breathing etc., and can further develop into two types of complications: one of which occurs with apnea of premature birth infants, also known as apnea of prematurity (AOP); the other is sudden infant death syndrome (SIDS) or apparent life threatening event (ALTE). If AOP is not properly diagnosed and treated, premature infants diagnosed with this type of symptom will be highly susceptible to SIDS and are accident-prone at home. Cessation of breathing might lead to hemodynamic chain reactions such as slowdown of the heartbeat rate, and even lowered blood pressure. These changes in hemodynamics can induce temporary loss of blood and oxygen to critical organs, especially to the brain cells and may even cause permanent damage to them. In clinical trials, premature infants often become stable in all other aspects and could be discharged from the hospital, if it were not for this type of irregular apnea symptom.
Infant monitors currently in clinical use are based on traditional bedside monitors of patients' physical condition and use three electrodes attached to the skin of the infant's chest, acquiring the signals from the changes in the chest impedance by breathing and heartbeat signals; these two signals are then converted into the separate breathing frequency and heartbeat rate by the filter. A major drawback of this type of monitoring technology is that prolonged contact with the sensor plates will cause skin redness, sensitivity, or deterioration; furthermore, monitors used clinically are often expensive and therefore not suitable for home caretaking purposes.
To solve the above-mentioned problem, U.S. Pat. No. 4,738,264 disclosed a vibration measurement apparatus that is separated from the patient and is disposed on the bed. The main principle behind the apparatus is that tiny vibrations of the body surfaces from normal breathing and heartbeat are transferred to the measurement apparatus through the bed, and then the apparatus converts the signals into a comprehensive energy index to represent the infant's breathing and heartbeat conditions. The drawback of this technique is that it cannot accurately distinguish and measure the infant's breathing frequency and heartbeat rate, and therefore cannot fulfill the clinical requirements for detecting the AOP alert threshold (i.e. breathing frequency is less than 20/minute of breathing ceases for over 15 seconds, and heartbeat rate is less than 80/minute).
In addition, U.S. Pat. No. 5,964,720 disclosed a distributed vibration measurement system that uses the piezoelectric crystals as the vibration sensors and uses strips of conducting film as the base of the sensors. These conductive strips can be embedded in the bed mattresses, seat backs, or cushions to detect tiny vibrations of the body surface resulting from normal breathing and the heartbeat of the patient. The major drawback of this technique is that the heart and chest vibration signals captured by the sensors tend to be subject to interference from vibration noise from the surroundings that travel through the human body and bed or seat to the sensor.